Composition and Corrosion Resistance of Chromate Passive Film on Electroless Plated Ni-P Alloy

An ultra-thin passive film was obtained on electroless plated Ni-P coating by treatment with a single agent chromate bath.Electrochemical tests indicated that the passivation treatment dramatically improved the corrosion resistance of the coating.The chemical composition of the passive film was analyzed with X-ray photoelectron spectroscopy(XPS),the result showed that the film comprised of O,Cr and Ni.According to the sputtering rate of Ar+ to the film,the thickness of the film was evaluated as about 6nm.By analyzing the high-resolution spectrum for the Cr 2p,it was found that the Cr in passive film was existed as trivalent compounds in the form of Cr2O3 and Cr(OH)3 And according to the XPS analysis,the formation mechanism of the passive film was discussed.